A gutter that is full of leaves and debris cannot function the way it was intended to. The accumulation of leaves and debris will stop the rain water to running efficiently along the gutter and into the drain pipe and down into the drain. This in turn can cause the rainwater to come over the sides of the gutters and bypass the downpipe which can cause damage to wood and the landscape below.
During winter months, this standing water can freeze and the extra weight can make the gutter belly out and can cause damage to the roof and in many cases cause the guttering to ultimately fall to the ground. All of these issues can be avoided by having your guttering cleaned on a regular basis.